This invention relates to machines for placing laths in packages of lumber.
Finished lumber is typically shipped from sawmills in packages. All lumber in a package is typically of the same thickness, width, length and quality. A typical package may be 2xc2xd feet tall, approximately 3xc2xd to 4xc2xd feet wide and 6 to 20 feet long. Such a package could comprise, for example, 20 layers of 1.5 inch thick lumber with, for example, 12, 13 or 14 pieces of 3xc2xd inch wide lumber per layer. A single mill may produce packages having different widths, depending upon the requirements of the mill""s customers. Packages of lumber are assembled by hand or with stacking machines. There are a number of different types of stacking machines in current use.
In order to preserve the integrity of a package of lumber during and after shipment, laths are typically placed transversely in the package. Laths may be placed transversely, for example, after every seven to ten layers of the package. The laths are thin strips of material that extend transversely across the package. Thin strips of wood are typically used for laths. Cardboard and other materials are sometimes used for laths. Each set of laths in a package may comprise, for example, three laths, one in the middle of the package and one near each end of the package.
After the package has been assembled, the package is typically strapped together with plastic or metal straps which extend around the package near the laths. The straps which hold a package of lumber together are typically tight. It has been found that these straps can warp the lumber if they are not aligned over the locations at which the laths are placed in the package. Finally, the package may be wrapped with a plastic wrap to protect the lumber during shipment.
Stacking machines are typically designed to handle laths of a length which is equal to the greatest width of packages to be assembled. When the stacking machine is assembling packages which are narrower than this maximum width, then the laths typically end up projecting out from at least one side of a package. The projecting lath ends prevent placement of the straps exactly in line with the laths. Before the package can be wrapped an operator typically breaks off the projecting ends of the laths.
A customer of the assignee of this invention recently proposed that, instead of placing a single lath across the width of a package the same objective could be realized by providing two shorter lath segments which overlap in the middle of the package. Ends of the lath segments could be aligned with outside edges of the package. Packages of different widths could be accommodated in this system by varying the degree of overlap of the lath segments. A strap could be wrapped around the package directly over the lath segments.
There were no existing lath placing machines capable of placing pairs of overlapping lath segments at spaced-apart locations along a package. There is a need for such machines.
This invention provides a lath placing machine. One aspect of the invention provides a lath placer comprising at least one lath placement section, the lath placement section comprising first and second lath segment placers. Each of the first and second lath placers comprise: a magazine capable of holding a plurality of laths; and, a lath picker operative to pick an uppermost lath from the magazine and drop the lath down a guide chute. The first and second lath segment placers are oriented transversely, and are movable relative to one another in a transverse direction.
In some embodiments the guide chutes of both of the first and second lath segment placers are between the magazines of the first and second lath segment placers. The magazine may be movable between a first position wherein an uppermost lath in the magazine is in line with the lath picker and a second position wherein a side of the magazine defines an edge of the guide chute and the lath picker is over the guide chute.
In some embodiments the first lath segment placer is be fixed in a transverse direction relative to a lumber stacker while the second lath segment placer is transversely movable relative to the lumber stacker. In some embodiments, the first and second lath segment placers are movable longitudinally relative to the lumber stacker.
Preferably each of the first and second lath segment placers comprises a lath gate at a lower end of the guide chute and the lath segment placer comprises a control system configured to open the lath gate to deposit a lath on a package of lumber.
In some embodiments of the invention, the first and second lath segment placers are oriented at a skew angle "PHgr" to a perpendicular to a centerline of a lumber stacker. The skew angle may be less than 12 degrees in some such embodiments. For example, in certain embodiments the skew angle is in the range of 4 to 9 degrees.
Another aspect of the invention provides a lath placer comprising at least one lath placement section, the lath placement section comprises first and second lath segment placers. Each of the first and second lath placers comprises: a magazine capable of holding a plurality of laths; a lath picker operative to pick an uppermost lath from the magazine and drop the lath down a guide chute; and, a lath gate located at a lower end of the guide chute. The first and second lath segment placers are oriented transversely and overlap one another and the lath gates of the first and second lath placers are both located between the magazines of the first and second lath placers.
Another aspect of the invention provides a method for automatically placing one or more pairs of transversely overlapping lath segments on a package of lumber. The method comprises: providing a plurality of lath segments in each of first and second transversely oriented overlapping magazines; picking an uppermost lath segment from each of the first and second magazines; dropping the picked lath segments down corresponding first and second guide chutes onto corresponding first and second lath gates, the first and second lath gates being located between the first and second magazines; and, opening the first and second lath gates to allow the lath segments to fall onto a package of lumber.
Further aspects of the invention and features of lath placing machines and methods according to specific embodiments of the invention are described below.